Tailored heat transfer layered heater system

ABSTRACT

Methods of assembling a high heat transfer and tailored heat transfer layered heater systems are provided. One method includes a step of pressing one of a target part and a layered heater into the other one of the target part and the layered heater to create an interference fit between the layered heater and the target part. When the target part is disposed within the layered heater, the layered heater includes a substrate defining an inner periphery less than or equal to an outer periphery of the target part. When the layered heater is disposed within the target part, the layered heater includes a substrate defining an outer periphery larger than or equal to an inner periphery of the target.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of application Ser. No.10/752,358, titled “Tailored Heat Transfer Layered Heater System” filedJan. 6, 2004. The disclosure of the above application is incorporatedherein by reference.

FIELD

The present disclosure relates generally to electrical heaters and moreparticularly to methods of controlling the heat transfer of electricalheaters.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Layered heaters are typically used in applications where space islimited, when heat output needs vary across a surface, where rapidthermal response is desirous, or in ultra-clean applications wheremoisture or other contaminants can migrate into conventional heaters. Alayered heater generally comprises layers of different materials,namely, a dielectric and a resistive material, which are applied to asubstrate. The dielectric material is applied first to the substrate andprovides electrical isolation between the substrate and theelectrically-live resistive material and also reduces current leakage toground during operation. The resistive material is applied to thedielectric material in a predetermined pattern and provides a resistiveheater circuit. The layered heater also includes leads that connect theresistive heater circuit to an electrical power source, which istypically cycled by a temperature controller. The lead-to-resistivecircuit interface is also typically protected both mechanically andelectrically from extraneous contact by providing strain relief andelectrical isolation through a protective layer. Accordingly, layeredheaters are highly customizable for a variety of heating applications.

Layered heaters may be “thick” film, “thin” film, or “thermallysprayed,” among others, wherein the primary difference between thesetypes of layered heaters is the method in which the layers are formed.For example, the layers for thick film heaters are typically formedusing processes such as screen printing, decal application, or filmdispensing heads, among others. The layers for thin film heaters aretypically formed using deposition processes such as ion plating,sputtering, chemical vapor deposition (CVD), and physical vapordeposition (PVD), among others. Yet another series of processes distinctfrom thin and thick film techniques are those known as thermal sprayingprocesses, which may include by way of example flame spraying, plasmaspraying, wire arc spraying, and HVOF (High Velocity Oxygen Fuel), amongothers.

In layered heater applications where the substrate is disposed around orwithin the part or device to be heated, such as that disclosed in U.S.Pat. No. 5,973,296, which is commonly assigned with the presentapplication and the contents of which are incorporated herein byreference in their entirety, intimate contact between the substrate andthe part to be heated is highly desirable in order to improve heattransfer between the layered heater and the part and thus overall heaterresponse. In known layered heaters, however, at least some small air gapis present between the substrate and the part due to inherent fittolerances, which negatively impacts heat transfer and the response ofthe layered heater. Other known heaters employ another material onassembly of the substrate to the part, for example, a compound in theform of a thermal transfer paste that is applied between the substrateand the part. During initial operation, however, this compound oftenproduces smoke that could contaminate the heater and/or the surroundingenvironment. Additionally, application of the compound is time consumingand may also result in some remaining air gaps.

In addition to improved heat transfer as described above, it is oftendesirable to vary the temperature profile or wattage distribution ofelectric heaters for certain applications. One known approach to obtaina variable wattage distribution is to vary the width and/or spacing of aresistive circuit pattern within an electric heater. The pattern may bea constant width trace with closer spacing in areas where more heat isdesired and wider spacing in areas where less heat is desired.Additionally, the width of the trace may be varied in order to achievethe desired wattage distributions. However, these forms of tailoring thetemperature profile or wattage distribution of electric heaters alsosuffer from reduced, unpredictable, and unrepeatable heat transfercharacteristics when undesirable air gaps are present between the heaterand the part.

SUMMARY

In one form, a method of the present disclosure comprises assembling atarget part and a layered heater to create an interference fit usingmechanical processes such as a press or a drive process, and thermalprocesses such as direct welding or heating/cooling of the target partand/or the substrate of the layered heater system. Further, methods ofassembling heater systems in order to provide a high heat transfer fitor a tailored heat transfer interface between a layered heater and atarget part are provided according to the teachings of the presentdisclosure.

For example, a method of forming a layered heater is provided thatcomprises forming a dielectric layer, forming a plurality of insulativepads on the dielectric layer, and forming a resistive layer over theinsulative pads and the dielectric layer. Such a method results in aheater system having a tailored heat transfer fit. Additionally, anothermethod employs a pre-coat, which is in one form a brazing compound,applied to either a target part and/or a layered heater in order toprovide a high heat transfer fit between the target part and the layeredheater.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the disclosure, are intended forpurposes of illustration only and are not intended to limit the scope ofthe disclosure.

DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 a is a side view of layered heater constructed in accordance withthe principles of the present disclosure;

FIG. 1 b is an enlarged partial cross-sectional side view, taken alongline A-A of FIG. 1 a, of a layered heater constructed in accordance withthe principles of the present disclosure;

FIG. 2 a is a side cross-sectional view of a layered heater disposedaround a hot runner nozzle according to a prior art heater system;

FIG. 2 b is a detail view, taken along detail B of FIG. 2 a, of an airgap and inconsistent heat transfer paths between a layered heater and ahot runner nozzle according to a prior art heater system;

FIG. 2 c is a cross-sectional view, taken along line C-C of FIG. 2 b,illustrating a non-concentric fit between a layered heater and a targetpart according to a prior art heater system;

FIG. 3 a is a side cross-sectional view of a layered heater and a targetpart constructed in accordance with the principles of the presentdisclosure;

FIG. 3 b is a side cross-sectional view of a layered heater disposedaround a target part in accordance with the principles of the presentdisclosure;

FIG. 3 c is a detail view, taken along detail D of FIG. 3 b, of aninterference fit between a layered heater and a target part inaccordance with the principles of the present disclosure;

FIG. 3 d is a cross-sectional view, taken along line E-E of FIG. 3 c, ofa concentric fit between a layered heater and a target part inaccordance with the principles of the present disclosure;

FIG. 4 a is a side cross-sectional view of a layered heater and a targetpart constructed in accordance with the principles of the presentdisclosure;

FIG. 4 b is a side cross-sectional view of a layered heater disposedwithin a target part in accordance with the principles of the presentdisclosure;

FIG. 5 a is a side cross-sectional view of a square layered heaterdisposed around a square target part in accordance with the principlesof the present disclosure;

FIG. 5 b is a side cross-sectional view of a square layered heaterdisposed within a square target part in accordance with the principlesof the present disclosure;

FIG. 6 is a side cross-sectional view of an oval layered heater disposedaround an oval target part in accordance with the principles of thepresent disclosure;

FIG. 7 is a side cross-sectional view of a rectangular layered heaterdisposed around a rectangular target part in accordance with theprinciples of the present disclosure;

FIG. 8 is a side cross-sectional view of a splined layered heaterdisposed within a splined target part in accordance with the principlesof the present disclosure;

FIG. 9 is a side cross-sectional view of a layered heater and a targetpart having a tapered configuration in accordance with the principles ofthe present disclosure;

FIG. 10 a is a side cross-sectional view of a recess created on an outersurface of a target part of a heater system and constructed inaccordance with the principles of the present disclosure;

FIG. 10 b is a side cross-sectional view of a recess created on an innersurface of a layered heater of a heater system and constructed inaccordance with the principles of the present disclosure;

FIG. 10 c is a side cross-sectional view of a recess created on an outersurface of a target part and on an inner surface of a layered heater ofa heater system, and further of a filler material and a discretecomponent within the recess, in accordance with the principles of thepresent disclosure;

FIG. 10 d is a side cross-sectional view of recesses created on an outersurface of a target part and on an inner surface of a layered heater ofa heater system and constructed in accordance with the principles of thepresent disclosure;

FIG. 11 is a side cross-sectional view of a heater system comprisingthermal spacers disposed between a target part and a layered heater;

FIG. 12 a is a side cross-sectional view of a heater system comprising alayered heater having a pre-coat and a target part in accordance withthe principles of the present disclosure;

FIG. 12 b is a side cross-sectional view of a heater system having ahigh heat transfer fit between a layered heater and a target part inaccordance with the principles of the present disclosure;

FIG. 13 is a side cross-sectional view of a heater system comprising athick film layered heater directly formed on a transfer substrate with atarget part disposed on the transfer substrate opposite the layeredheater; and

FIG. 14 is a side cross-sectional view, taken longitudinally along aresistive layer trace, illustrating insulative pads in accordance withthe teachings of the present disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

The following description of the present disclosure is merely exemplaryin nature and is in no way intended to limit the disclosure, itsapplication, or uses.

Referring to FIGS. 1 a and 1 b, a layered heater system in accordancewith the present disclosure is preferably employed with a layeredheater, which is illustrated and generally indicated by referencenumeral 10. The layered heater 10 comprises a number of layers disposedon a substrate 12, wherein the substrate 12 may be a separate elementdisposed proximate the part or device to be heated, or the substrate 12may be the part or device itself. As best shown in FIG. 1 b, the layerspreferably comprise a dielectric layer 14, a resistive layer 16, and aprotective layer 18. The dielectric layer 14 provides electricalisolation between the substrate 12 and the resistive layer 16 and isformed on the substrate 12 in a thickness commensurate with the poweroutput, applied voltage, intended application temperature, orcombinations thereof, of the layered heater 10. The resistive layer 16is formed on the dielectric layer 14 and provides a heater circuit forthe layered heater 10, thereby providing the heat to the substrate 12.The protective layer 18 is formed on the resistive layer 16 and ispreferably an insulator, however other materials such as an electricallyor thermally conductive material may also be employed according to therequirements of a specific heating application while remaining withinthe scope of the present disclosure.

As further shown, terminal pads 20 are preferably disposed on thedielectric layer 14 and are in contact with the resistive layer 16.Accordingly, electrical leads 22 are in contact with the terminal pads20 and connect the resistive layer 16 to a power source (not shown).(Only one terminal pad 20 and one electrical lead 22 are shown forclarity, and it should be understood that two terminal pads 20 with oneelectrical lead 22 per terminal pad 20 is the preferred form of thepresent disclosure). The terminal pads 20 are not required to be incontact with the dielectric layer 14 and thus the illustration of theembodiment in FIG. 1 is not intended to limit the scope of the presentdisclosure, so long as the terminal pads 20 are electrically connectedto the resistive layer 16 in some form. As further shown, the protectivelayer 18 is formed on the resistive layer 16 and is preferably adielectric material for electrical isolation and protection of theresistive layer 16 from the operating environment. Additionally, theprotective layer 18 may cover a portion of the terminal pads 20 as shownso long as there remains sufficient area to promote an electricalconnection with the power source.

As used herein, the term “layered heater” should be construed to includeheaters that comprise at least one functional layer (e.g., dielectriclayer 14, resistive layer 16, and protective layer 18, among others),wherein the layer is formed through application or accumulation of amaterial to a substrate or another layer using processes associated withthick film, thin film, thermal spraying, or sol-gel, among others. Theseprocesses are also referred to as “layered processes,” “layeringprocesses,” or “layered heater processes.” Such processes and functionallayers are described in greater detail in co-pending application titled“Combined Layering Technologies for Electric Heaters,” filed on Jan. 6,2004, which is commonly assigned with the present application and thecontents of which are incorporated herein by reference in theirentirety.

Referring now to FIG. 2 a, a prior art heater system 30 is illustrated,which comprises a layered heater 32 disposed around a hot runner nozzle34 of an injection molding system. The layered heater 32 is generallyappropriately sized to enable a “slip-fit,” or an interference fit, overthe hot runner nozzle 34, wherein the layered heater 32 is slid with arelatively low physical resistance over the hot runner nozzle 34 atambient or room temperature for assembly. Unfortunately, this “slip-fit”results in an air gap 36 between the layered heater 32 and the hotrunner nozzle 34, which reduces the heat transfer characteristicsbetween the layered heater 32 and the hot runner nozzle 34. In addition,this type of fit makes the heat transfer characteristics of the heatingsystem 30 difficult to repeat and reproduce from part to part and frombatch to batch. The presence of the air gap 36 and the resultant loss inheat transfer causes a slower response of the layered heater system 30,which negatively impacts the performance of the heater system 30. Asshown in greater detail in FIG. 2 b, even if the fit between the layeredheater 32 and the hot runner nozzle 34 were relatively close, air gaps36 still remain and only intermittent conductive heat transfer atlocations 38 are present. Therefore, air gaps 36 are undesirable in suchheater systems due to the degradation of heat transfer. Additionally, asshown in FIG. 2 c, the clearance fit often results in non-concentricpositioning of the layered heater 32 relative to the hot runner nozzle34. This non-concentric fit produces even more pronounced air gaps 36,which further degrade the performance of the heater system 30.

Accordingly, a heater system 40 as shown in FIGS. 3 a-3 c is provided bythe present disclosure in order to improve the heat transfer between alayered heater 42 (not all layers are shown for purposes of clarity) anda part that is to be heated, which is hereinafter referred to as atarget part 44. As shown, both the layered heater 42 and the target part44 are preferably cylindrical, although other shapes are contemplated bythe present disclosure as described in greater detail below. The layeredheater 42 comprises a substrate 46 that defines a room temperature innerdiameter D1 that is less than or equal to a room temperature outerdiameter D2 of the target part 44. The room temperature inner diameterD1 may be sized to be equal to D2 in the application of a line-to-linefit of the layered heater 42 to the target part 44. Therefore, thelayered heater 42 is assembled with the target part 44 using eithermechanical or thermal methods in order to create an interference fit 48as best shown in FIGS. 3 b and 3 c. The interference fit 48 thus resultsin improved heat transfer between the layered heater 42 and the targetpart 44, thereby improving the response of the layered heater 42.

Moreover, as shown in FIG. 3 d, a concentric fit between the layeredheater 42 and the target part 44 is produced as a result of theinterference fit 48. As the layered heater 42 is thermally ormechanically formed around the target part 44, as described in greaterdetail below, the outer diameter of the target part 44 conforms to theinner diameter of the layered heater 42, which positions the layeredheater 42 and the target part 44 concentrically as shown. Thisconcentric fit further reduces the air gaps, provides more uniform heattransfer, and thus improves the response of the layered heater 42.

The preferred mechanical methods to create the interference fit 48include a press or a drive process, although other processes known inthe art may also be employed while remaining within the scope of thepresent disclosure. The thermal methods may include, but are not limitedto, cooling and/or heating the target part 44 and/or the layered heater42. For example, the target part 44 may be cooled while the layeredheater 42 remains at room temperature, thereby reducing the roomtemperature outer diameter D2 such that the target part 44 may bepositioned within the layered heater 42. Upon return to roomtemperature, the target part 44 expands back towards the roomtemperature outer diameter D2 to create the interference fit 48.Alternately, the layered heater 42 may be heated while the target part44 is cooled, or the layered heater 42 may be heated while the targetpart 44 remains at room temperature.

As shown in FIGS. 4 a and 4 b, the layered heater 42 is alternatelypositioned within the target part 44 rather than around the target partas previously illustrated. Accordingly, the layered heater 42 comprisesa room temperature outer diameter D3, and the target part 44 defines aroom temperature inner diameter D4 such that upon application of amechanical or thermal process as previously described, the interferencefit 48 is formed between the layered heater 42 and the target part 44.

Referring to FIGS. 5 through 8, the layered heater 42 and the targetpart 44 need not necessarily be cylindrical in shape, and other shapesare also contemplated within the scope of the present disclosure whereinthe interference fit 48 is created between a layered heater and a targetpart. These shapes may include, by way of example, a square shape 50 asshown in FIGS. 5 a and 5 b, an oval shape 52 as shown in FIG. 6, arectangular shape 54 as shown in FIG. 7, or a curved shape 56 as shownin FIG. 8, or combinations thereof. Accordingly, as shown for example inFIG. 5 a, a layered heater 60 comprises a substrate 62 defining a roomtemperature inner periphery 64, and a target part 66 defines a roomtemperature outer periphery 68, wherein the room temperature innerperiphery 64 of the layered heater 60 is less than or equal to the roomtemperature outer periphery 68 of the target part 66. As a result of themechanical or thermal processes as previously described, an interferencefit 70 is created between the layered heater 60 and the target part 66,thereby improving the heat transfer characteristics between the layeredheater 60 and the target part 66. Alternately, as shown in FIG. 5 b, thelayered heater 60 may be disposed within the target part 66 rather thanoutside the target part 66 as shown in FIG. 5 a, wherein a roomtemperature outer periphery 72 of the layered heater 60 is greater thanor equal to a room temperature inner periphery 74 of the target part 66.Although layered heaters 60′ and 60″ are shown disposed around targetparts 66′ and 66″, respectively, in FIGS. 6 and 7, and layered heater60′″ within the target part 66′″ in FIG. 8, the layered heaters mayeither be disposed around or within these target parts as specificapplications dictate while remaining within the scope of the presentdisclosure. It should be understood that the shapes and configurationsas shown and described herein are exemplary and should not be construedas limiting the scope of the present disclosure to only those shapes andconfigurations.

Referring now to FIG. 9, the present disclosure further contemplatesgeometry that comprises a non-constant cross-section as shown with alayered heater 76 disposed around a target part 78 in a taperedconfiguration. Generally, the target part 78 and the layered heater 76are brought into engagement and the tapered configuration facilitatesboth concentricity and the interference fit for improved heat transfer.As a result of the tapered configurations, the layered heater 76 and thetarget part 78 may be assembled and disassembled with greater ease overthe alternate forms having a constant cross-section as previouslydescribed. More specifically, only a relatively small lineardisplacement of the layered heater 76 with respect to the target part 78is required to engage and disengage the layered heater 76 and the targetpart 78 due to the tapered configuration. An interference fit 79therefore results between the layered heater 76 an the target part 78using a mechanical self-locking taper in one form of the presentdisclosure. Additionally, thermal methods as previously described mayalso be employed to produce the interference fit 79. Moreover, thelayered heater 76 may alternately be disposed within the target part 78while remaining within the scope of the present disclosure.

In another form of the present disclosure as shown in FIGS. 10 a-10 d, atailored heat transfer system 78 is provided by the present disclosurethat includes both high heat transfer characteristics with theinterference fit as previously described, in addition to impeded, orselectively restricted, heat transfer characteristics along the lengthof the heater system 78, thereby resulting in tailored heat transfercharacteristics. More specifically, as shown in FIG. 10 a, a layeredheater 80 is disposed around a target part 82, wherein a recess 84 isdisposed therebetween. The recess 84 provides for local restricted heattransfer characteristics along the length of the layered heater 80 inapplications where such tailored control may be required. Additionally,although only one recess 84 is illustrated herein, it should beunderstood that a plurality of recesses may also be employed whileremaining within the scope of the present disclosure. Therefore, thetailored heat transfer system 78 comprises at least one recess 84 inaccordance with the teachings of the present disclosure.

As further shown, the resistive layer 16 may also be altered along thelength of the layered heater 80 to provide additional tailoring of theheat transfer characteristics, in addition to the tailoring provided bythe recess 84. The illustration of the resistive layer 16 is thusexemplary and should not be construed as limiting the scope of thepresent disclosure. Additionally, an interference fit 86 is createdbetween the layered heater 80 and the target part 82 as previouslydescribed, thereby creating improved heat transfer characteristicsbetween the layered heater 80 and the target part 82 in those areas. Therecess 84 as shown in FIG. 10 a is an outer surface recess within thetarget part 82, however, other forms of creating the recess 84 andmultiple recesses and alternate locations are shown in FIGS. 10 b-10 c.

As shown in FIG. 10 b, the recess 84 is an inner surface recess withinthe substrate 12 of the layered heater 80. Both an inner surface recesswithin the layered heater 80 and an outer surface recess within thetarget part 82 are shown in FIG. 10 c to create the recess 84.Alternately, both inner surface recesses 84′ within the layered heater80 and an outer surface recess 84″ within the target part 82 are shownin FIG. 10 d, wherein multiple recesses in alternate locations along thelength of the heater system 78 are provided. It should be understoodthat the layered heaters 80 may alternately be disposed within thetarget parts 82 and may also take on alternate shapes as previouslyillustrated while remaining within the scope of the present disclosure.

As further shown in FIG. 10 c by way of example, the tailored heattransfer system 78 in another form comprises a filler material 88disposed within the recess 84 for altering the heat transfer propertiesproximate the recess 84. The filler material 88 may be insulative orconductive for either lower or higher heat transfer characteristics asdesired. For example, in one form the filler material 88 may be a liquidmetal for higher heat transfer or a salt or Sauereisen® cement for lowerheat transfer. In yet another form, the tailored heat transfer system 78comprises a discrete component 89 disposed within the recess 84 toperform certain functions that may be desired. For example, the discretecomponent 89 may be a thermocouple for temperature sensing local to adesired area. Additional discrete components may include, but are notlimited to, RTDs (Resistance Temperature Detectors), thermistors, straingauges, thermal fuses, optical fibers, and microprocessors andcontrollers, among others. Therefore, the heat transfer system 78provides improved heat transfer characteristics, impeded heat transfercharacteristics, and discrete functional capabilities according to theteachings of the present disclosure.

Referring to FIG. 11, yet another form of the present disclosure thatprovides tailored heat transfer via selectively improved and/or impededheat transfer is illustrated as heater system 90. The heater system 90comprises a layered heater 92 disposed proximate a target part 94,wherein a plurality of thermal spacers 96 are disposed between thelayered heater 92 and the target part 94. As a result, a plurality oftailored heat transfer regions 98 and 99 are formed for tailored heattransfer. Heat transfer region 98 is illustrated between the thermalspacers 96 and the layered heater 92 and target part 94, and the heattransfer region 99 is illustrated between the layered heater 92 and thetarget part 94. The heat transfer regions 98 and 99 may thus be tailoredfor improved and/or impeded heat transfer, wherein for example, if thethermal spacers 96 were conductive, heat transfer region 98 wouldprovide improved heat transfer and heat transfer region 99 would provideimpeded heat transfer.

Preferably, the thermal spacers 96 have a coefficient of thermalexpansion (CTE) greater than that of the layered heater 92, morespecifically the substrate of the layered heater which is not shownherein for clarity, and the target part 94. Accordingly, the thermalspacers 96 expand during operation to create a high heat transfer fit 98between the layered heater 92 and the target part 94 proximate thethermal spacers 96. In one form, the thermal spacers 96 are an aluminummaterial, however, other materials may also be employed while remainingwithin the scope of the present disclosure.

Alternately, an interference fit as previously described may be employedwith the heater system 90, wherein mechanical or thermal processes areemployed to create the interference fit and thus provide for improvedheat transfer characteristics in desired areas. For example, the thermalspacers 96 would define a room temperature thickness T that is greaterthan or equal to the room temperature distance D between the layeredheater 92 and the target part 94. The thermal spacers 96 may be formedon the target part 94 using processes such as thermal spraying, or thethermal spacers 96 may alternately be formed on the layered heater 92also using the process of thermal spraying. It should be understood thatother processes may also be employed to form the thermal spacers 96while remaining within the scope of the present disclosure. Therefore,the heater system 90 provides improved heat transfer characteristics andimpeded heat transfer characteristics according to the teachings of thepresent disclosure.

Yet another form of the present disclosure is illustrated in FIGS. 12 aand 12 b, wherein a heater system 100 comprises a layered heater 102comprising a substrate 104 with a pre-coated surface 106. The pre-coatedsurface 106 is preferably coated with a brazing material, however, othermaterials may also be employed while remaining within the scope of thepresent disclosure. As shown, an inner diameter D5 of the layered heater102 is less than or equal to an outer diameter D6 of a target part 108.Therefore, either the mechanical or thermal processes may be employed aspreviously described in order to create a high heat transfer fit 110between the layered heater 102 and the target part 108. Additionally,the layered heater may be disposed inside the target part and othershapes may be employed as previously described while remaining withinthe scope of the present disclosure. Other variations of treating thelayered heater 102 and/or the target part 108 in order to create a highheat transfer fit shall be construed as falling within the scope of thepresent disclosure. These variations may include, by way of example,direct welding (e.g., friction stir welding), among others.

Referring now to FIG. 13, another form of the present disclosure thatprovides improved heat transfer is illustrated and shown as heatersystem 120. In this form, a thick film layered heater 122 is formeddirectly on a heated surface 124 of a heat transfer substrate 126. Atarget part 128 that is formed of a material which is directlyincompatible with the thick film layered heater 122 is disposed on theheat transfer substrate 126 as shown, opposite the thick film layeredheater 122. Accordingly, the heat transfer substrate 126 transfers heatfrom the thick film layered heater 122 to the target part 128 and thus athick film layered heater 122 may be employed with a previouslyincompatible target part 128. “Directly incompatible” as used herein isdirected to the combination of a thick film layered heater and a targetpart, wherein the difference in CTE between the thick film layeredheater and the target part is relatively large such that this large CTEdifference would cause degradation in the structural integrity of thethick film heater. Additionally, the high firing temperatures of thethick film layered heater would be too high for the target part thatconsists of a material incapable of withstanding heater layer processingtemperatures. Moreover, the high firing temperatures of the thick filmlayered heater may alter material properties of the target part, forexample, where the target part comprises a heat treated surface thatwould be altered during firing. Therefore, “directly incompatible” meansa large CTE difference between the thick film layered heater and thetarget part, a target part that is incapable of withstanding the highfiring temperatures of the thick film layered heater, and/or a targetpart comprising a material that would be altered during firing.

Additionally, the target part 128 may be disposed outside the heattransfer substrate 126 and the layered heater 122 disposed within theheat transfer substrate 126, as previously illustrated, while remainingwithin the scope of the present disclosure. Further, an interference fitbetween the heat transfer substrate 126 and the target part 128 may alsobe formed as described herein without departing from the spirit andscope of the present disclosures. Moreover, alternate shapes may beemployed, as previously illustrated, according to specific applicationrequirements without departing from the teachings of the presentdisclosure.

As shown in FIG. 14, another form of the present disclosure thatprovides tailored heat transfer characteristics is shown and illustratedas a heater system 130. The heater system 130 comprises a layered heater132 disposed around a target part 134, although the layered heater 132could alternately be disposed within the target part 134. The layeredheater 132 further comprises a dielectric layer 136, which shown formeddirectly on the target part 134, however, the dielectric layer 136 mayalternately be formed on a substrate with an interference fit betweenthe substrate and the target part 134 as previously described. Asfurther shown, a plurality of insulative pads 138 are formed on thedielectric layer 136, and a resistive layer 140 is formed over theinsulative pads 138, followed by a protective layer 142 formed over theresistive layer 140. The insulative pads 138 are disposed between theresistive layer 140 and the target part 134 to reduce the rate of heattransfer from the resistive layer 140 to the target part 134 asrequired. Alternately, the insulative pads 138 may be disposed betweenthe resistive layer 140 and the protective layer 142 to reduce the rateof heat transfer to the surrounding environment. Therefore, theinsulative pads 138 are employed to further tailor the heat transfercharacteristics along the layered heater 132.

The description of the disclosure is merely exemplary in nature and,thus, variations that do not depart from the gist of the disclosure areintended to be within the scope of the disclosure. The layered heatersas shown and described herein may be disposed within or around thetarget part, various geometric configurations may be employed, and theelements for tailored heat transfer may be employed at various locationsthroughout the layered heater system. Additionally, the heater systemsas described herein may be employed with a two-wire controller as shownand described in co-pending application Ser. No. 10/719,327, titled“Two-Wire Layered Heater System,” filed Nov. 21, 2003, and in co-pendingapplication titled “Combined Material Layering Technologies for ElectricHeaters,” filed Jan. 6, 2004, both of which are commonly assigned withthe present application and the contents of which are incorporatedherein by reference in their entirety. Such variations are not to beregarded as a departure from the spirit and scope of the disclosure.

1. A method of assembling a heater system comprising the steps of: (a)thermally treating at least one of a target part defining a roomtemperature outer periphery and a layered heater comprising a substratedefining a room temperature inner periphery such that the respectiveperiphery is dimensionally altered; (b) positioning the target partwithin the layered heater; and (c) bringing at least one of the targetpart and the layered heater to room temperature, thereby causing aninterference fit between the layered heater and the target part toproduce in a concentric fit between the layered heater and the targetpart.
 2. The method according to claim 1 wherein the thermally treatingcomprises cooling the target part.
 3. The method according to claim 1wherein the thermally treating comprises cooling the target part andheating the layered heater.
 4. The method according to claim 1 whereinthe thermally treating comprises heating the layered heater.
 5. Themethod according to claim 1 further comprising forming a dielectriclayer as a part of the layered heater, forming a plurality of insulativepads on the dielectric layer, and forming a resistive layer over theinsulative pads.
 6. The method according to claim 5 further comprisingforming a protective layer over the resistive layer.
 7. A method ofassembling a heater system comprising the steps of: (a) thermallytreating at least one of a target part defining a room temperature innerperiphery and a layered heater defining a room temperature outerperiphery such that the respective periphery is dimensionally altered;(b) positioning the target part around the layered heater; and (c)bringing at least one of the target part and the layered heater to roomtemperature, thereby causing an interference fit between the layeredheater and the target part to produce in a concentric fit between thelayered heater and the target part.
 8. The method according to claim 7wherein the thermally treating comprises cooling the layered heater. 9.The method according to claim 7 wherein the thermally treating comprisescooling the layered heater and heating the target part.
 10. The methodaccording to claim 7 wherein the thermally treating comprises heatingthe target part.
 11. The method according to claim 7 further comprisingforming a dielectric layer as a part of the layered heater, forming aplurality of insulative pads on the dielectric layer, and forming aresistive layer over the insulative pads.
 12. The method according toclaim 11 further comprising forming a protective layer over theresistive layer.
 13. A method of assembling a layered heater systemcomprising the steps of: (a) coating at least one surface of a targetpart or a layered heater with a pre-coat; and (b) positioning the targetpart proximate the layered heater such that the pre-coat is disposedbetween the target part and the layered heater, wherein the pre-coatprovides a high heat transfer fit between the target part and thelayered heater.
 14. The method according to claim 13, wherein thepre-coat is a brazing material.
 15. The method according to claim 13,wherein the pre-coat is applied to an outer surface of the target partand the pre-coat is disposed between the outer surface of the targetpart and an inner surface of the layered heater.
 16. The methodaccording to claim 13, wherein the pre-coat is applied to an innersurface of the target part and the pre-coat is disposed between theinner surface of the target part and an outer surface of the layeredheater.
 17. The method according to claim 13, wherein the pre-coat isapplied to an inner surface of the layered heater and the pre-coat isdisposed between the inner surface of the layered heater and an outersurface of the target part.
 18. The method according to claim 13,wherein the pre-coat is applied to an outer surface of the layeredheater and the pre-coat is disposed between the outer surface of thelayered heater and an inner surface of the target part.
 19. A method offorming a layered heater comprising forming a dielectric layer, forminga plurality of insulative pads on the dielectric layer, and forming aresistive layer over the insulative pads and the dielectric layer. 20.The method according to claim 20 further comprising forming a protectivelayer over the resistive layer.
 21. The method according to claim 19,wherein the dielectric layer is formed directly onto a target part.